cmd/compile: internal compiler error: unexpected types2.Invalid

[meln5674]

Go version

go version go1.24.1 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/andrew/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/andrew/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2188541391=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/andrew/git/src/github.com/meln5674/goj-compiler-bug/go.mod'
GOMODCACHE='/home/andrew/git/pkg/mod'
GONOPROXY='github.com/meln5675/*'
GONOSUMDB='github.com/meln5675/*'
GOOS='linux'
GOPATH='/home/andrew/git/'
GOPRIVATE='github.com/meln5675/*'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go-1.24.1'
GOSUMDB='sum.golang.org'
GOTELEMETRY='off'
GOTELEMETRYDIR='/home/andrew/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go-1.24.1/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

https://go.dev/play/p/oCCeMP7r2Jk

This is not the original source this defect was discovered in, which is not publicly releasable. The above was derived by removing source elements until the error no longer occurred and then anonymizing names.

A few previous versions of go that I happened to have installed were spot checked across 1.23 and 1.22 and they all produced internal errors, so this is likely not a regression in 1.24.1 .

What did you see happen?

Received the following error message:

# <REDACTED: root package of module>
<unknown line number>: internal compiler error: unexpected types2.Invalid

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

This occurs identically locally and in the linked go playground.

What did you expect to see?

The command to either succeed or produce a usable error message.

[randall77]

The command to either succeed or produce a usable error message.

Any idea which one? I cannot fathom whether this is legal Go code or not.

[meln5674]

I am fairly certain this is legal, as the original code base compiled and executed correctly until a single new field was added, which, unsurprisingly, ended up as the "B" field in the anonymized example. go fmt works without issue, so it is at very least syntactically legal.

[gabyhelp]

Related Issues

• internal compiler error: bad type for ... argument: [2]string #45913 (closed)
• cmd/compile: internal compiler error when processing invalid recursive type #49276 (closed)
• cmd/compile: random compile error running tests #35760 (closed)
• cmd/compile: internal compiler error: unexpected type uint for 1 #32959 (closed)
• cmd/compile: internal compiler error: unexpected stmt: nil #50315 (closed)
• cmd/compile: internal compiler error with zero-size types #65808 (closed)
• [dev.typeparams] internal compiler error: cannot export = (22) node #47514 (closed)
• cmd/compile: internal compiler error: Type.Elem UNION #58345 (closed)
• cmd/compile: internal compiler error: bad Sym: have M, want foo #49017 (closed)
• cmd/compile: internal compiler error: unexpected dot in identifier: .anon0 #25101 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[meln5674]

I have managed to simplify it further, along with a clearer naming scheme that disambiguates between types, fields, and type params: https://go.dev/play/p/bKryWGDZIep .

This makes it more obvious that there is a cycle in the type graph between B and D, which I originally believed to be the issue, but curiously, removing A fixes the error, as does making D a typedef for B directly or making B an alias for a pointer to D. It seems that it is this specific graph shape that triggers the bug.

[meln5674]

Further progress: https://go.dev/play/p/5Pkrr97m2QT has an identical shape, but doesn't have the error. The only difference is that B is changed to a typedef of C, instead of an alias. I traced this back to what this represented in the original codebase, changed it from an alias to a typedef, and the original codebase compiles again. Something about that edge in the graph being an alias instead of a typedef must be the cause.

[ianlancetaylor]

When using the alias these programs look invalid to me. They contain an invalid circular reference.

CC @griesemer @findleyr

[meln5674]

Can you elaborate? B and D do not actually contain eachother in their representations, they are both empty structs by virtue of being an alias/typedef to C and E respectively, The reference is only in the type parameters. For example https://go.dev/play/p/yuQ_x9x_tA7 is valid, despite having the same circular reference in type parameters, and even having one (but not both) of the type edges be an alias.

[ianlancetaylor]

A type alias means that you can substitute the name being defined with the right hand side. In the example https://go.dev/play/p/bKryWGDZIep after we substitute for TypeB we have type TypeD TypeE[TypeC[*TypeD]]. So TypeD is being defined in terms of itself. That's not the case when not using an alias: without the alias, there are different types that refer to each other.

That said, there are some cases where circular type definitions are OK. I suppose I don't really know whether this is one of them.

[findleyr]

This panic was added in https://go.dev/cl/338973, in response to #25838.

Panicking stack:

runtime/debug.Stack()
	runtime/debug/stack.go:26 +0x5e
cmd/compile/internal/base.FatalfAt({0x139040?, 0xc0?}, {0xec4422, 0x19}, {0x0, 0x0, 0x0})
	cmd/compile/internal/base/print.go:230 +0x1ea
cmd/compile/internal/base.Fatalf(...)
	cmd/compile/internal/base/print.go:195
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000139040, {0x102b790, 0x15d9440}, 0xc000116500)
	cmd/compile/internal/noder/writer.go:533 +0x597
cmd/compile/internal/noder.(*writer).typ(0xc0003f5080, {0x102b790?, 0x15d9440?})
	cmd/compile/internal/noder/writer.go:481 +0x2f
cmd/compile/internal/noder.(*writer).doObj(0xc0003f5080, 0xc0003f5130, {0x10341e0, 0xc0004009c0})
	cmd/compile/internal/noder/writer.go:883 +0x318
cmd/compile/internal/noder.(*pkgWriter).objIdx(0xc000139040, {0x10341e0, 0xc0004009c0})
	cmd/compile/internal/noder/writer.go:815 +0x84b
cmd/compile/internal/noder.(*pkgWriter).objInstIdx(0xc000139040, {0x10341e0, 0xc0004009c0}, 0x0, 0xc000116460)
	cmd/compile/internal/noder/writer.go:756 +0xf4
cmd/compile/internal/noder.(*writer).obj(0xc0003f4fd0, {0x10341e0?, 0xc0004009c0?}, 0xc0001350a0?)
	cmd/compile/internal/noder/writer.go:730 +0x33
cmd/compile/internal/noder.(*writer).namedType(0xc0003f4fd0, 0xc0004009c0, 0x0)
	cmd/compile/internal/noder/writer.go:631 +0x52
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000139040, {0x102b6c8, 0xc0001350a0}, 0xc000116460)
	cmd/compile/internal/noder/writer.go:550 +0x8cc
cmd/compile/internal/noder.(*writer).typ(0xc0003f4f20, {0x102b6c8?, 0xc0001350a0?})
	cmd/compile/internal/noder/writer.go:481 +0x2f
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000139040, {0x102b678, 0xc000036bb0}, 0xc000116460)
	cmd/compile/internal/noder/writer.go:578 +0x875
cmd/compile/internal/noder.(*pkgWriter).objInstIdx(0xc000139040, {0x10341e0, 0xc000400960}, 0xc0003fe3a8, 0xc000116460)
	cmd/compile/internal/noder/writer.go:754 +0x99
cmd/compile/internal/noder.(*writer).obj(0xc0003f4e70, {0x10341e0?, 0xc000400960?}, 0xc0001351f0?)
	cmd/compile/internal/noder/writer.go:730 +0x33
cmd/compile/internal/noder.(*writer).namedType(0xc0003f4e70, 0xc000400960, 0xc0003fe3a8)
	cmd/compile/internal/noder/writer.go:631 +0x52
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000139040, {0x102b6c8, 0xc0001351f0}, 0xc000116460)
	cmd/compile/internal/noder/writer.go:550 +0x8cc
cmd/compile/internal/noder.(*writer).typ(0xc0003f4bb0, {0x102b6c8?, 0xc0001351f0?})
	cmd/compile/internal/noder/writer.go:481 +0x2f
cmd/compile/internal/noder.(*writer).doObj(0xc0003f4bb0, 0xc0003f4c60, {0x10341e0, 0xc000400900})
	cmd/compile/internal/noder/writer.go:873 +0x4c5
cmd/compile/internal/noder.(*pkgWriter).objIdx(0xc000139040, {0x10341e0, 0xc000400900})
	cmd/compile/internal/noder/writer.go:815 +0x84b
cmd/compile/internal/noder.(*pkgWriter).objInstIdx(0xc000139040, {0x10341e0, 0xc000400900}, 0x0, 0xc0001163c0)
	cmd/compile/internal/noder/writer.go:756 +0xf4
cmd/compile/internal/noder.(*writer).obj(0xc0003f4b00, {0x10341e0?, 0xc000400900?}, 0x1?)
	cmd/compile/internal/noder/writer.go:730 +0x33
cmd/compile/internal/noder.(*writer).namedType(0xc0003f4b00, 0xc000400900, 0x0)
	cmd/compile/internal/noder/writer.go:631 +0x52
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000139040, {0x102b6f0, 0xc0003fcf00}, 0xc0001163c0)
	cmd/compile/internal/noder/writer.go:554 +0x3e5
cmd/compile/internal/noder.(*writer).typ(0xc0003f4a50, {0x102b6f0?, 0xc0003fcf00?})
	cmd/compile/internal/noder/writer.go:481 +0x2f
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000139040, {0x102b678, 0xc000036b50}, 0xc0001163c0)
	cmd/compile/internal/noder/writer.go:578 +0x875
cmd/compile/internal/noder.(*writer).typ(0xc0003f46e0, {0x102b678?, 0xc000036b50?})
	cmd/compile/internal/noder/writer.go:481 +0x2f
cmd/compile/internal/noder.(*writer).doObj(0xc0003f46e0, 0xc0003f4790, {0x10341e0, 0xc0004008a0})
	cmd/compile/internal/noder/writer.go:883 +0x318
cmd/compile/internal/noder.(*pkgWriter).objIdx(0xc000139040, {0x10341e0, 0xc0004008a0})
	cmd/compile/internal/noder/writer.go:815 +0x84b
cmd/compile/internal/noder.(*pkgWriter).objInstIdx(0xc000139040, {0x10341e0, 0xc0004008a0}, 0x0, 0x0)
	cmd/compile/internal/noder/writer.go:756 +0xf4
cmd/compile/internal/noder.(*writer).obj(0xc0003f44d0, {0x10341e0?, 0xc0004008a0?}, 0x0?)
	cmd/compile/internal/noder/writer.go:730 +0x33
cmd/compile/internal/noder.writePkgStub({0x0?, {0x0?, 0x0?}}, {0xc0000686c0, 0x1, 0x1})
	cmd/compile/internal/noder/unified.go:343 +0x6fa
cmd/compile/internal/noder.unified({0x0?, {0x0?, 0x0?}}, {0xc0000686c0?, 0xdd9ce0?, 0x0?})
	cmd/compile/internal/noder/unified.go:195 +0xb3
cmd/compile/internal/noder.LoadPackage({0xc000020170, 0x1, 0x1})
	cmd/compile/internal/noder/noder.go:77 +0x43a
cmd/compile/internal/gc.Main(0xeeca88)
	cmd/compile/internal/gc/main.go:208 +0xcc5

[findleyr]

Without digging too deeply, the problem seems to be that go/types creates a Typ[Invalid] without reporting an actual error. My guess is there is some inaccurate "error reported elsewhere" assumption.